The invention generally relates to controlling the actual fuel delivered to individual combustion chambers and, more particularly, the individual control of combustion chamber air/fuel ratios.
Feedback control systems are known for controlling the average air/fuel ratio of the engine in response to a single oxygen sensor coupled to the engine exhaust manifold. More specifically, open loop control is first established by simultaneously varying the pulse width of all fuel injector drive signals the same amount in relation to a measurement of airflow inducted into the engine. Feedback control is then established by further adjusting all the drive signals simultaneously by the same amount in response to the exhaust gas oxygen sensor thereby achieving a desired average air/fuel ratio. A problem with this approach is that the air/fuel ratio is an average of the individual air/fuel ratios of each combustion chamber. A variation in air/fuel ratios among the combustion chambers is most likely For example, each fuel injector may actually deliver a different quantity of fuel when actuated by the identical drive signal due to such factors as manufacturing tolerances, component wear, and clogging. Even though known feedback control systems may achieve the desired average air/fuel ratio, the variations in air/fuel ratios among combustion chambers may result in less than optimal power, driveability, and emission control.
An approach to controlling air/fuel ratios of the individual combustion chambers is disclosed in U.S. Pat. No. 4,483,300 issued to Hosaka et al. In simplified terms, fluctuations in the exhaust gas sensor signal are examined to detect cylinder to cylinder distribution of the air/fuel ratio. A disadvantage of this approach is that a very fast exhaust gas oxygen sensor is required to detect variations in the exhaust output of each cylinder. A further disadvantage is that because exhaust output of each cylinder is mixed in an exhaust manifold, the signal to noise ratio with respect to each cylinder is very low requiring complex signal processing techniques. Another disadvantage of this approach is the complexity of the computations and microprocessor capability required. Since a typical engine microprocessor must control numerous engine functions, the memory available for storing additional program codes is severely limited. Accordingly, the approach disclosed by Hosaka et al may not be suitable for a large number of automobile applications.